1. Field of the Invention
The present invention relates to a semiconductor device, and in particular, to a semiconductor device having a sealing resin portion that seals a semiconductor element.
2. Description of the Background Art
Semiconductor devices include a power semiconductor device having a mold resin (sealing resin portion) as disclosed in Japanese Patent Laying-Open No. 2003-264265, for example. According to this publication, the power semiconductor device has a semiconductor element, a metal block, a lead frame, and a casing. The semiconductor element has a surface and a back surface. The metal block is fixed to the back surface of the semiconductor element. The lead frame is fixed by soldering to the surface of the semiconductor element. The semiconductor element, the metal block and the lead frame are integrally-molded by the mold resin of the casing.
The foregoing publication describes that, according to a configuration of this power semiconductor device, the mold resin surrounds the lead frame and the semiconductor element, so that junction therebetween can be strengthened and fatigue failure in a connecting portion of the lead frame is less likely.
In the above power semiconductor device, however, in a case where the semiconductor device generates heat or the usage environment of the semiconductor device changes, fatigue failure due to thermal stress applied to a soldered portion occurs in some cases.
This thermal stress is caused by a difference in linear expansion coefficient between components of the semiconductor device. As an example of the difference in linear expansion coefficient, silicon used for the semiconductor element has a linear expansion coefficient of approximately 2.3×10−6 (1/K), copper used for an electrode lead has a linear expansion coefficient of approximately 16.7×10−6, and a sealing resin has a linear expansion coefficient of approximately 18×10−6. As a result of the thermal stress caused by such difference in linear expansion coefficient, fatigue failure in a joining portion of the lead frame (electrode lead) is more likely.